This invention relates generally to ball valves for controlling fluid flow and, more particularly, to a ball valve having an improved valve seat assembly constructed of concentric seat rings which enclose and energize a resilient sealing element.
Heretofore, in the manufacture of ball valves, valve seats are typically constructed of a single piece annular seat ring having a press fit resilient sealing ring in a face thereof. The valve seats are placed in valve seat pockets such that the sealing rings contact the ball valve member. However, in this type of construction, the mounting of the sealing ring in the seat ring is often difficult in that the sealing ring must be press fit into a groove in the seat ring or it must be placed into a groove in the seat ring and, then, the seat ring deformed to grip or secure the sealing ring. These types of construction are undesirable from a manufacturing standpoint because in the first case once the sealing ring is press fit into the groove it is difficult to remove or replace and, in the second case, it is difficult to determine the force necessary to deform the seat ring into gripping engagement with the sealing ring. Therefore, in these types of construction, field replacement of the sealing ring requires replacement of the complete valve seat assembly resulting in increased production costs.
A valve seat utilizing two concentric seat rings emcompassing a replaceable sealing ring is also not necessarily new in the art. One type of valve seat assembly constructed in this manner is described in U.S. Pat. No. 4,071,041 assigned to the same assignee as the present application. However, In U.S. Pat. No. 4,071,041 the concentric seat rings are held together by separate locking means, thereby, requiring extra manufacturing steps to complete the valve seat assembly. Furthermore, the seat rings do not positively lock and energize the sealing ring between them, thereby, allowing line pressure to get behind the sealing ring causing its extrusion under high pressure.